Process for sugar extraction



United States Patent ()flice 3,135,631 PROCESS FOR SUGAR EXTRACTEQN Emirhan Vahdettin Gulharan, Universite, Fen Falrultesi, Ankara, Turkey No Drawing. Filed Feb. 5, 1962, Ser. No. 171,243 6 (Iiairns. (Cl. 127-4l3) This invention relates to a process for extracting sugar from sugar-containing material, such as sugar beets and sugar cane. More particularly, this invention relates to an improved method of leaching sugar from the sugarcontaining material by an alteration of the conventional diflusion processes.

Many of the presently used and known processes for separating sugar from sugar-containing materials are not applicable both to sugar cane and sugar beets. Most plants today have a diiierent procedure for each of these two materials. The presently employed method for separating sugar from sugar cane involves the passing of shredded cane between heavy rollers, which exert great pressure upon the cane, squeezing the juices therefrom. During the pressing operation, water is circulated between the rollers to wash away the extracted sugar. The diffusion process is the method most generally used for extracting sugar from sugar beets. In this process, the beets are cut into slices, and the sugar is extracted from the slices by countercurrent flow of hot water, leaving a pulp containing approximately 0.3 to 0.5 percent sugar. Neither the processes used for sugar cane nor those used for sugar beets can effect an essentially complete extraction of the sugar from the sugar-containing material in a reasonable time and at reasonable cost.

The sugar-containing materials also contain substantial quantities of pectins. If the pectins are extracted with the sugar, the sugar solution becomes extremely difficult to process in subsequent steps. The presently known sugar-extraction processes invariably extract some pectin along with the sugar.

The diifusion process of the prior art takes approximately 75 to 110 minutes, to reduce the sugar-containing material to a concentration of about 0.3 to 0.5 percent sugar.

Thus, there is a need in the art for a process that is applicable either to sugar cane, sugar beets, or other sugarcontaining materials. There is also a need for a process that will substantially shorten the time required for sugar extraction and, in the shortened time period, will result in an improved extraction of the sugar from the sugarcontaining material. There is also a need in the art for a sugar-extraction process that will produce a sugar solution that is essentially free of pectin.

It is an object of this invention to provide a process that will extract sugar from any sugar-containing material.

It is another object of this invention to provide a process that substantially shortens the time for extracting sugar from sugar-containing materials.

A further object of this invention is to provide a process that will remove substantially all of the sugar from the sugar-containing material in a reasonable period of time and at reasonable cost.

It is still another object of this invention to provide a sugar-extraction process that produces a sugar solution that is essentially free of pectin.

Another object of this invention is to reduce the time required for the extraction of sugar from sugar cane and sugar beets to the order of 25 minutes.

Yet another object of this invention is to provide a process capable of producing any desired concentration of sugar in the syrup product.

The objects of this invention are accomplished by a process now to be described. This process for the extrac- 3,135,631 Patented June 2, 1964 tion of sugar from sugar-containing materials comprises the steps of: reducing sugar-containing material to a thickness of not greater than 0.5 centimeter; subjecting the sugar-containing material to an absolute pressure in the range of about 350 to 380 millimeters of mercury for a period of about 2 to 5 minutes; immersing the sugarcontaining material in an aqueous solution, maintained at a temperature of from about to C. for a period of about 2 to 5 minutes; removing the sugar-containing material from the aqueous solution; percolating water at a temperature of from about 75 to 85 C. through a bed of said sugar-containing material, said bed having a depth not greater than 20 centimeters, until the residual sugar content of the bed material is not greater than 0.3 percent by weight; maintaining an absolute pressure in the range of from about 350 to 380 millimeters of mercury during all of the above steps subsequent to recluction in size; and collecting the sugar-containing water resulting from the above steps. The steps of this process will now be discussed in further detail.

The process is equally applicable to any sugarcontaining material, such as sugar cane, sugar beets, etc. To prepare the sugar-containing material for the extraction step, the material must be reduced in size to a thickness of not greater than 0.5 centimeter. This reduction in size is necessary so that the time for the leaching and diffusion steps will not be unduly long. While the process would be operable on sections thicker than 0.5 centimeter, the time required for extraction of the sugar from such sections would be impractically long. At the same time, the use of sections thinner than 0.5 centimeter will result in faster extraction times. When slices become too thin, however, they become unwieldy and also the sugar-containing cells are ruptured and impurities contained therein are permitted to escape and contaminate the collection solution. The optimum slice thickness to achieve maximum extraction speed and minimum contamination from impurities has been found to be between 0.1 to 0.2 centimeter. The above figures are primarily applicable to sugar beets, since sugar cane is difficult to section. It has been found that the simplest way to handle sugar cane is to reduce it to a powder and process it in this form. The powder is formed relatively easily by feeding the sugar cane into rotating blades.

After the sugar-containing material has been reduced to an appropriate size for subsequent handling, it is subjected to a pressure in the range of from about 350 to 380 millimeters of mercury for a period of about 2 to 5 minutes. Treating the sugar-containing material in this manner not only improves the extraction, but also decreases the time required for extraction. It has been found that varying the pressure from a subatmospheric pressure in the range of from 350 to 380 millimeters to atmospheric during this step still further enhances the extraction. By varying the pressure in the manner hereinbefore mentioned, the extraction of sugar from the sugar-containing material is improved by as much as 9 to 10 percent in the same period of time. With longer material holding times during a given step, the desired enhancement of extraction may be achieved by releasing vacuum once approximately every five minutes. The sugar-containing material is in essentially a dry condition during this step, since water has not been added.

' The degree of sugar extraction and the time required for this extraction have been found to be substantially enhanced by conducting the previous step and all of the subsequent steps, until the sugar has been extracted, at a pressure in the range of from about 350 to 380 millimeters oi mercury. Still further improvement in the separation is noted when the pressure is varied from a subatmospheric pressure in the range of from about 350 to 380 millimeters to atmospheric pressure. It is important that this change in pressure occur (such as by releasing the vacuum) at least once during the preceding step of the process and during each of the subsequent steps. If desired, this change in pressure can take place several times during any of the individual steps of the process. However, substantial improvement in the separation results, even with only one such variation during any given step. This change in pressure can be brought about by any of the conventional techniques. Among these are pumping and steam ejection.

Following the step where the unwetted sugar-containing material is subjected to a variation in pressure, the sugar-containing material is then immersed in an aqueous solution maintained at a temperature of from about 75 to 85 C. for a period of about 2 to 5 minutes. In this step, it is important to regulate the temperature as close to this range as possible. Above 82 C., peptization occurs, and there is an increase in the extraction of pectins. As discussed above, the pressure is varied at least once during this step, from 350-380 millimeters to atmospheric. While two minutes in the aqueous solution may be sufiicient for thinner sections, up to five minutes may be required for thicker slices of the sugar-containing material. Approximately half of the sugar in the sugar-containing material is extracted in this step. When the solution reaches a concentration of approximately 12-13 percent sugar, the syrup solution is drawn off. Since the concentration of the subsequent leaching solution is also approximately 13 percent, if desired, the solution from this step may be added thereto. If higher concentrations are desired the process is continued longer before the syrup is drawn off.

The sugar-containing material is next removed from the aqueous solution. In a batch-type operation, the solution would merely be drawn off and the sugar-containing material would remain. In a continuous process, any convenient conveying means may be employed for transferring the sugar-containing material from the aqueous solution. For example, the sugar-containing material could be conveyed through the solution and the speed of the conveyor so arranged that the residence time in the solution would be of the order of two to five minutes. After removal from the aqueous solution, the sugarcontaining material is arranged in a bed having a depth not greater than 20 centimeters. Water, at a temperature of about 75 to 85 C. is then percolated through this bed of sugar-containing material. Ideally, this water should be at a temperature of about 80 0, since, at this temperature, a minimum amount of pectin is removed from the sugar-containing material. When the bed depth is greater than 20 centimeters, the time required for extraction of the sugar is unduly extended. Beds of shallower depth, of course, decrease the time required for extraction. The preferred bed depth is approximately 15 centimeters. It is important to note here the difference between the process of this invention and those of the prior art. In the prior art, the water flows countercurrently to the passage of the sugar-containing material. Consequently, the concentration gradient between the solution contacting the sugar-containing material and the material itself is relatively small. It is the concentration gradient between the solution and the sugar-containing material that determines the rate of diflfusion. In this process by percolating fresh water through a bed of sugar-containing material, the concentration gradient between the water and the sugar-containing material is always at a maximum. Water is permitted to percolate through the bed of sugar-containing material until the residual sugar content is not greater than 0.3 percent by weight. The residual sugar content of the bed material can readily be determined by analytical means. For example, the refractive index is an easily measured property that can serve as a guide to the sugar content of the bed material. It has been found that, by the process of this invention, essentially all of the sugar can be removed from the sugar-containing material in a period of about 25 minutes. The processes of the prior art require about 75 to 110 minutes to extract all but 0.3 percent. Since the process of this invention is so rapid, it is both practical and economical to continue the percolation of water through the bed of sugar-containing material until the residual sugar content essentially reaches zero. However, when the residual sugar content of the bed material reaches 0.3 percent, which requires less than 25 minutes, the process has equaled the extraction result of the prior art methods. Again, during this percolation step, the pressure is varied between subatmospheric pressure and atmospheric pressure, as described above. Where the process is practiced on a batch basis, the sugar-containing material can readily be subjected to percolation in a column. On a continuous basis, the bed of sugar-containing material can be conveyed under a series of water sprays that provide a suflicient quantity of water to remove the desired amount of sugar.

As previously mentioned, the water used to leach the sugar from the sugar-containing material should be maintained at a temperature of about C. to reduce peptization and pectin removal. Pectin removal is also minimized when the pH of the water is about 5. Accordingly, where it is desired to have a pectin-free sugar solution, the pH of the water used for leaching is adjusted to about 5.

The water percolated through the bed of sugar-containing material, whether on a batch basis or on a continuous basis by a series of spray nozzles, is collected in a receiver. This water contains the sugar extracted in the process. From a process cost standpoint, the amount of water used to leach the sugar from the material should be controlled so that the final sugar concentration of the water collected is about 13 percent. This is approximately the concentration of solutions obtained from the present processes.

Where the pH of the water used in leaching has been adjusted to 5, to prevent pectin removal, upon collection of the sugar solution, the pH must be adjusted back to the alkaline side. The pH should be adjusted to the range of from 7 to 8. Any conventional alkaline material may be used for this purpose. At an acid pH, inversion of the sucrose to fructose and glucose would occur.

So that the process may be better understood, the following specific example is set forth; while these examples are intended to be illustrative, they are not intended to establish limitations of the invention.

Example 1 Sugar beets were sliced to produce slices having a total weight of grams. The average thickness of the slices was about 0.1 centimeter. These slices were placed in a column until a depth of the bed was about 15 centimeters. The air in the column was brought to a temperature of about 80 C. by means of a heat exchanger wrapped around the column. Vacuum was then intermittently applied to the column for five minutes. The pressure in the column was brought to somewhere in the range of from about 350 to 380 millimeters of mercury. During the processing of this batch of sugar beet slices, the vacuum was released each five minutes and the system brought to atmospheric pressure. After applying vacuum to the sugar beet slices for five minutes, and then releasing the vacuum to bring the system to atmospheric pressure, water was added to the system until the sugar beet slices were totally immersed. This water was at a temperature of about 80 C. Again, vacuum was applied until the pressure was about 380 millimeters. After about five minutes, the pressure was released, and the water drained from the column. Water at a temperature of about 80 C. and adjusted to a pH of about 5 was then permitted to percolate through the bed of sugar beet slices. Vacuum was applied until the pressure reached about 380 millimeters and then released each five minutes. The percolation of water was stopped approximately 25 minutes after the sugar beet slices were first subjected to vacuum prior to wetting. The pH of the sugar solution collected was adjusted to the alkaline side by means of calcium hydroxide. Samples from the residue in the column were then removed for analysis by refractometer and then by polarimeter. These analyses indicated that no sugar remained in the residue in any part of the column after this period of time. The concentration of sugar in the solution collected from the column Was approximately 13 percent by weight.

Example II When sugar cane is cut to form a powder and substituted for the sugar beet slices used in Example I and the same procedure followed, similar results were obtained. The sugar cane powder was placed in the column to a bed depth of about 15 centimeters. Water percolation was again stopped after 25 minutes. The residue in the column analyzed by refractometer and then by polarimeter showed no sugar.

Example 111 The procedure of Example I was repeated, using continuous vacuum rather than intermittent vacuum. To remove essentially all of this sugar from the sugar beet slices required approximately 4-0 minutes. This represented a marked improvement over the prior art processes, but was not as fast as the use of intermittent vacuum.

Example IV Six series of tests were run to obtain a comparison of the extraction obtained when continuous and intermittent vacuum were used during the extraction steps. The extraction time for each of the comparative tests was the same, the only difference being that during the one case the vacuum was continuous, and in the other case the vacuum was released each five minutes. The following percentages of sugar were recovered in these tests: (Each figure represents an average of ten tests.)

[Sugar recovered, percent] Test Series A B C I D I E F Continuous Vacuum 11.2 11.0 10.8 10.1 10.0 11.1 Intermittent Vacuum 12.1 13.1 11.2 10. 7 11.0 12.0

The above data show that the use of intermittent vacuum, as opposed to continuous vacuum, increases the extraction of sugar by about 9 percent.

Example V of not greater than 0.5 centimeter, subjecting the sugarcontaining material of reduced thickness to pressure in the range of from about 350 to 380 millimeters of mercury for a period of about 2 to 5 minutes, immersing the pressure subjected sugar-containing material for a period of about 2 to 5 minutes in water under pressure in the range of from about 350 to 380 millimeters of mercury and at temperature of from about 75 to 85 C. and collecting the sugar-containing Water and removing the solid residue of the sugar-containing material from the sugarcontaining water, and percolating a further supply of water at a temperature of from about 75 to 85 C. through a bed of said residue of the sugar-containing material under pressure in the range of from about 350 to 380 millimeters of mercury and having depth not greater than 20 centimeters until the residual sugar content of the bed material is at most about 0.3 percent by weight and collecting the sugar-containing water from said bed.

2. In a process for sugar extraction, the art which includes, reducing sugar-containing material to a thickness of not greater than 0.5 centimeter, subjecting the sugar-containing material of reduced thickness to pressure varied from atmospheric to 350-380 millimeters of mercury for a period of about 2 to 5 minutes, immersing the pressure subjected sugar-containing material for a period of about 2 to 5 minutes in water under pressure varied from atmospheric to 350-380 millimeters of mercury and at temperature of from about 75 to 85 C. and collecting the sugar-containing water and removing the solid residue of the sugar-containing material from the sugar-containing water, and percolating a further supply of water at temperature of from about 75 to 85 C. through a bed of said residue of the sugarcontaining material under pressure varied from atmospheric to 350-380 millimeters of mercury and having depth not greater than 20 centimeters until the residual sugar content of the bed material is at most about 0.3

percent by weight and collecting the sugar-containing water from said bed.

3. In a process forsugar extraction, the art which includes, reducing sugar-containing material to a thickness of not greater than 0.5 centimeter, subjecting the sugar-containing material of reduced thickness to pressure intermittently varied from atmospheric to about 350-380 millimeters of mercury for a period of about 2 to 3 minutes, immersing the pressure subjected sugar- It is advisable to begin the extraction process with v sugar beets as soon after slicing as possible. It has been observed that the slices become tacky upon prolonged standing and are difiicult to handle.

The total production achievable by this process is limited only by the size of the equipment that can be de signed and built. Of course, where desired, more than one production line can be employed.

This is a continuation-in-part of US. patent application Serial No. 114,920, filed June 5, 1961, now abandoned.

What is claimed is:

1. In a process for sugar extraction, the art which incontaining material for a period of about 2 to 5 minutes in water under pressure varied from atmospheric to 350- 380 millimeters of mercury and at temperature of from about 75 to 85 C. and collecting the sugar-containing water and removing the solid residue of the sugar-com taining material from the sugar-containing water, and percolating a further supply of water having pH of about 5 and temperature of from about 75 to 85 C. through a bed of said residue of the sugar-containing material under pressure varied from atmospheric to 350-3 millimeters of mercury and having depth of not greater than about 15 centimeters until the residual sugar content of the bed material is at most about 0.1 percent by weight and collecting the sugar-containing water from said bed and adjusting the pH of the sugar-containing water collected from the bed to a value of about 7 to 8.

4. In a process for extracting sugar fromsugar beets, the art which includes, slicing sugar beets to a thickness of about 0.1 to 0.2 centimeter, subjecting the sugar beet slices having said thickness to pressure varied from atmospheric to about 380 millimeters of mercury for a period of about 2 to 3 minutes, immersing the pressure subjected sugar beet slices for a period of about 2 to 5 minutes in water under pressure varied from atmospheric to about 380 millimeters of mercury and at temperature or" about 80 C. and collecting the sugar-containing water and removing the solid residue of the beet slices from the sugar-containing water, and percolating a further supply of water at temperature of about 80 C. and adjusted to a pH of about 5 through a bed of said residue of the beet slices under pressure varied from atmospheric to about 380 millimeters of mercury and having depth of about 15 centimeters until the residual sugar content of said residue in the bed is at most about 0.1 percent by weight and collecting the sugar-containing water from said bed and adjusting the pH of the sugar-containing water from said bed to a value of about 7 to 8.

5. In a process for extracting sugar from sugar cane, the art which includes, reducing sugar cane to a powder, subjecting said sugar cane powder to pressure varied from atmospheric to about 380 millimeters of mercury for a period of about 2 to 3 minutes, immersing the pressure subjected sugar cane powder for a period of about 2 to 5 minutes in water under pressure varied from atmospheric to about 380 millimeters of mercury and at temperature of about 80 C. and collecting the sugarcontaining water and removing the solid residue of the sugar cane powder from the sugar-containing water, and percolating a further supply of water at temperature of about 80 C. and adjusted to a pH of about 5 through a bed of said residue of the sugar-containing powder under pressure varied from atmospheric to about 380 millimeters of mercury and having depth of about 15 centimeters until the residual sugar content of the residue of said sugar cane powder in the bed is at most 0.1 percent by weight and collecting the sugar-containing water 5.3 from said bed and adjusting the pH of said sugar-containing water collected from the bed to a value of about 7 to 8.

6. In a process for sugar extraction, the art which includes, sectioning a sugar-containing material to a thickness of less than about 0.5 centimeter, subjecting the sectioned sugar-containing material to subatmospherjic pressure and immersing the pressure subjected sugarcontaining material at subatmospheric pressure in water having a temperature lower than that at which peptization of sugar occurs and thus recovering in aqueous solution a substantial proportion of the sugar content from the sugar-containing material in said water, and separating the residue of the sugar-containing material from said aqueous solution and percolating a further supply of water of a temperature below that at which peptization of sugar occurs through a bed of said residue of the sugarcontaining material under subatmospheric pressure and collecting the water from the percolation treatment for extraction of the sugar therefrom.

References Cited in the file of this patent UNITED STATES PATENTS 1,617,962 Nobel Feb. 15, 1927 3,047,430 Goodban et a1 July 31, 1962 FOREIGN PATENTS 293,066 Great Britain Feb. 23, 1927 

1. IN A PROCESS FOR SUGAR EXTRACTION, THE ART WHICH INCLUDES, REDUCING SUGAR-CONTAINING MATERIAL TO A THICKNESS OF NOT GREATER THAN 0.5 CENTIMETER, SUBJECTING THE SUGARCONTAINING MATERIAL OF REDUCED THICKNESS TO PRESSURE IN THE RANGE OF FROM ABOUT 350 TO 380 MILLIMETERS OF MERCURY FOR A PERIOD OF ABOUT 2 TO 5 MINUTES IMMERSING THE PRESSURE SUBJECTED SUGAR-CONTAINING MATERIAL FOR A PERIOD OF ABOUT 2 TO 5 MINUTES IN WATER UNDER PRESSURE IN THE RANGE OF FROM ABOUT 350 TO 380 MILLIMETERS OF MERCURY AND AT TEMPERATURE OF FROM ABOUT 75* TO 85*C. AND COLLECTING THE SUGAR-CONTAINING WATER AND REMOVING THE SOLID RESIDUE OF THE SUGAR-CONTAINING MATERIAL FROM THE SUGARCONTAINING WATER, AND PERCOLATING A FURTHER SUPPLY OF WATER AT A TEMPERATURE OF FROM ABOUT 75* TO 85*C. THROUGH A BED OF SAID RESIDUE OF THE SUGAR-CONTAINING MATERIAL UNDER PRESSURE IN THE RANGE OF FROM ABOUT 350 TO 380 MILLIMETERS OF MERCURY AND HAVING DEPTH NOT GREATER THAN 20 CENTIMETERS UNTIL THE RESIDUAL SUGAR CONTENT OF THE BED MATERIAL IS AT MOST ABOUT 0.3 PERCENT BY WEIGHT AND COLLECTING THE SUGAR-CONTAINING WATER FROM SAID BED. 